Description of the Prior Art
The German OS No. 27 27 510 describes an anionic paper surface sizing material which attains its benefits by using copolymers of maleic anhydride and dicyclopentadiene which have been subsequently reacted with ammonia or primary or secondary amines in aqueous solution. The copolymer to be used is obtained in a known manner by polymerization in solution or suspension in the presence of radical catalysts.
It is also known to combine 4-vinyl-cyclohexene with maleic anhydride. In that case azobisisobutyronitrile is used as the catalyst. The applications of this copolymer have not been disclosed.
Russian Pat. No. 370,215 discloses a telomer which is produced by radical copolymerization of maleic anhydride, vinylcyclohexene and carbon tetrachloride. In the example the reaction is conducted for 20 hours at 65.degree.-70.degree. C. and yields ca. 43% of theoretical.
It is generally known to pulp size paper by using rosin soaps and aluminum ions. In addition to known rosin sizing, solutions or dispersions of polymeric compounds have proven effective in paper sizing. The advantage of such synthetic resin sizes is, among others, is that they can be applied to the finished paper surface while the usual resin size is precipitated onto the paper fibers with aluminum ions.
The use of synthetic polymer sizes makes it possible to size paper without adding metal salts. Solutions or dispersions of random copolymers of unsaturated carboxylic acids or their derivatives with certain ethylenically unsaturated compounds are particularly suited for sizes of that type. The level of sizing of papers sized with these copolymers of the prior art does not correspond in all cases, e.g., sizing pulp sized paper, to the technical requirements.
German OS No. 16 21 693 teaches that copolymers containing succinimide groups can be used to size paper surfaces, with vinylogous compounds used as comonomers. Dicyclopentadiene is mentioned as a possible vinylogous compound, among others. To make the described copolymers soluble for paper sizing they must be reacted with ammonia, alkalis or amines. A number of derivatives are produced thereby, due to the content of imide groups.
With the method mentioned above it is necessary, in order to produce the imide groups, either to convert maleic anhydride into maleic imide or afterward to form the imide groupings in a copolymer of maleic anhydride and vinylogs.
For economic reasons, however, it is desirable to simplify as far as possible the production of the copolymer used to size the paper, and for reasons of improved reproducibility to restrict the number of derivatives used in solubilizing them.